Radiocarbon dating is used to determine the age of carbon-bearing
material by measuring its radiocarbon, the radioactive isotope carbon-14
(with six protons and eight neutrons). Invented by Willard Libby in the
late 1940s, the method soon became a standard tool for archaeologists.
Radiocarbon is constantly created in the atmosphere, when cosmic rays
create free neutrons that hit nitrogen. Plants take in carbon, including
radiocarbon, through photosynthesis, and after an animal or plant dies,
it stops exchanging carbon with its environment. Half of the radiocarbon
decays every 5,730 years; the oldest dates that can be reliably measured
by radiocarbon dating are around 50,000 years ago. Atmospheric
radiocarbon was reduced starting in the late 19th century by fossil
fuels, which contain little detectable radiocarbon, but nuclear weapons
testing reversed that trend, almost doubling it by 1963. Accelerator
mass spectrometry has become the method of choice for radiocarbon
dating; it can be used with samples as small as plant grains. Libby
received the Nobel Prize for his work in 1960.
Read more: <https://en.wikipedia.org/wiki/Radiocarbon_dating>
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Today's selected anniversaries:
1663:
King Charles II of England granted John Clarke the Rhode Island
Royal Charter, described by one historian as "the grandest instrument of
human liberty ever constructed."
<https://en.wikipedia.org/wiki/Rhode_Island_Royal_Charter>
1709:
Great Northern War: Peter I of Russia defeated Charles XII of
Sweden in Poltava, effectively ending Sweden's role as a major power in
Europe.
<https://en.wikipedia.org/wiki/Battle_of_Poltava>
1808:
Joseph Bonaparte approved the Bayonne Statute, a royal charter
intended as the basis for his rule as King of Spain during the
Peninsular War.
<https://en.wikipedia.org/wiki/Bayonne_Statute>
1947:
After various news agencies reported the capture of a "flying
disc" by U.S. Army Air Force personnel in Roswell, New Mexico, the
military stated that what was actually recovered was debris from an
experimental high-altitude surveillance weather balloon.
<https://en.wikipedia.org/wiki/Roswell_UFO_incident>
2011:
Space Shuttle Atlantis was launched in STS-135, the final
mission of the U.S. Space Shuttle program.
<https://en.wikipedia.org/wiki/STS-135>
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Wiktionary's word of the day:
maw:
1. The upper digestive tract (where food enters the body), especially the
mouth and jaws of a ravenous creature.
2. Any great, insatiable or perilous opening.
<https://en.wiktionary.org/wiki/maw>
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Wikiquote quote of the day:
Bring me your children hither. … Unto this twain, man-child
and womanchild, I give the passion of this element; This seed of
longing, substance of this love; This power, this purity, this
annihilation. Let their hands light the altar of the world. 'T is yours
forever. I have brought it home!
--William Vaughn Moody
<https://en.wikiquote.org/wiki/William_Vaughn_Moody>